Experimental evidence of s-wave superconductivity in bulk CaC$_{6}$

TL;DR

This study provides experimental evidence that bulk CaC$_{6}$ exhibits s-wave superconductivity, characterized by an exponential temperature dependence of the magnetic penetration depth consistent with BCS theory.

Contribution

The paper presents direct experimental measurements of the magnetic penetration depth in CaC$_{6}$, confirming its isotropic s-wave pairing symmetry and providing key parameters consistent with conventional BCS superconductivity.

Findings

Exponential temperature dependence of $\lambda_{ab}(T)$ at low temperatures.

Estimated zero-temperature penetration depth $\lambda_{ab}(0)=(720\pm 80)$ Å.

Superconducting gap $\Delta(0)=(1.79\pm 0.08)$ meV and ratio $2\Delta(0)/k_B T_c \\approx 3.6$, indicating weak coupling.

Abstract

The temperature dependence of the in-plane magnetic penetration depth, $\lambda_{ab}(T)$, has been measured in a c-axis oriented polycrystalline CaC$_{6}$ bulk sample using a high-resolution mutual inductance technique. A clear exponential behavior of $\lambda_{ab}(T)$ has been observed at low temperatures, strongly suggesting isotropic s-wave pairing. Data fit using the standard BCS theory yields $\lambda_{ab}(0)=(720\pm 80)$ Angstroem and $\Delta(0)=(1.79\pm 0.08)$ meV. The ratio $2\Delta(0)/k_{_B}T_{c}=(3.6\pm 0.2)$ gives indication for a conventional weakly coupled superconductor.